Improvements in the capabilities of image data processing devices such as printers and digital cameras in recent years have been accompanied by utilization of color space of wider color gamuts in the processing of image data.
In a digital camera, for example, color correction processing is executed in a color space having a wide color gamut, examples of such a color space being sRGB and Adobe RGB. The flow of image processing in a digital camera having a color correction processing function disclosed in the specification of Japanese Patent Application Laid-Open No. 2003-198909 will be described with reference to FIG. 17 as an example of such processing.
As shown in FIG. 17, light is introduced to the lens of a digital camera in response to pressing of a shutter-release button (step S1701), and the incident light is made to impinge upon a sensor such as a CCD or CMOS so that the optical signal is converted to an RGB digital signal (step S1702).
Next, this digital image data is subjected to interpolation processing followed by processing such as white-balance processing (step S1703). The image data that has undergone interpolation processing is subjected to a color correction by sRGB color space or by the wider Adobe RGB color space based upon a designation made by the user (step S1704). (For reference purposes, the color gamuts of sRGB color space and Adobe RGB color space are indicated at 1601 and 1602 in FIG. 16.)
After the color-corrected image data is subjected to gamma processing in conformity with the monitor output (step S1705), the image data is subjected to JPEG (Joint Photographic Experts Group) compression (step S1706). One series of image processing operations is thus completed.
Thus, in the case of a digital camera, color correction processing utilizing a color space having a wide color gamut is executed in image processing up to the compression and storage of image data captured by photography.
In recent years, not only widening of color-space color gamut but also higher tonality is sought in processing of image data in an image data processing apparatus. For this reason, an improvement in the bit precision of image data processed is contemplated for, e.g., printers, for the purpose of widening the color gamut of color space and raising tonality.
In the case of a printer, however, when image data is subjected to print processing based upon a high bit precision, a problem which arises is that if the printing medium is of low quality, print processing takes an inordinately long period of time considering the low quality of the printed results. In other words, as far as the user is concerned, the desired printed result is not obtained despite the fact that print processing is executed over an extended period of time.
In view of these circumstances, lowering the bit precision has been considered as a measure to shorten the time needed for print processing. However, if bit precision is simply lowered under a wide color gamut, tonality will decline. That is, in a case where bit precision is raised in order to realize a wider color gamut and higher tonality in a printer, implementing this upon taking into account a balance between print-processing time and quality of printed results is preferred in view of suitability to user needs.
Similarly, in the case of a digital camera, it is necessary to take into account the balance between color gamut and tone in regard to realizing a wide color gamut and higher tonality. For example, as mentioned above, the color space used in the color correction of step S1704 is specified by the user. Since the JPEG scheme has a bit precision of eight bits, however, the color gamut of the captured image data will widen but tonality will decline if Adobe RGB color space is specified by the user. Such a decline in tonality becomes especially conspicuous in cases where the subject of photography is a human being.
More specifically, in a case where color-correction processing using sRGB color space and color-correction processing using Adobe RGB color space is performed with same bit precision, the color-correction processing using sRGB color space provides better tonality than the color-correction processing using Adobe RGB color space.
This means that in a case where the subject is something other than a human being, such as scenery, color gamut should be emphasized and Adobe RGB color space specified. On the other hand, if the subject is a human being, the tonality of skin color should be emphasized and sRGB color space should be specified.
Thus, with regard to widening color gamut and improving tonality in a digital camera, implementing this upon taking into account the nature of the subject is preferred in view of suitability to user needs.